1. Field of the Invention
The present invention relates to a discharge circuit for a smoothing capacitor of a DC power supply that is used in an electrical power conversion device of an inverter or the like.
2. Description of the Related Art
An inverter that is used for driving a motor of a hybrid automobile or the like has a function of converting DC power supplied from a DC power supply into AC power to be supplied to an AC electric load such as a rotating electrical machine or the like, and/or a function of converting AC electrical power generated by a rotating electrical machine into DC power to be supplied to a DC power supply. In order to fulfill these conversion functions, such an inverter is equipped with an electrical power conversion circuit that uses switching elements, and performs electrical power conversion from DC power into AC power, or from AC power into DC power, by repeatedly making these switching elements continuous and discontinuous.
In such an inverter, a high capacity DC power supply smoothing capacitor is provided for stabilizing voltage fluctuations of the DC power supply during operation. Furthermore, an interrupter such as a contactor or the like is provided between the battery and this DC power supply smoothing capacitor, so that, when the hybrid automobile is to be driven, a traveling motor can be powered by operating the inverter after the contactor has been closed (hereinafter, this is termed “turned ON”) and the capacitor has been charged up. On the other hand, when the hybrid automobile has been stopped, the contactor is opened (hereinafter, this is termed “turned OFF”) and then the capacitor is discharged via a discharge circuit.
A control device for an electric automobile is per se known with which, in order to determine whether there is any fault with the contactor or the discharge circuit for such an inverter, it is arranged to monitor the terminal voltage across the DC power supply smoothing capacitor from the time point that the hybrid automobile is stopped, and: it is decided that no fault is occurring if, when a certain time period T1 (for example, 40 seconds) has elapsed after the automobile has been stopped, the terminal voltage of the capacitor has not fallen below a predetermined value; it is decided that there is some fault with the discharge circuit if, when another certain time period T2 (for example, 5 minutes) has elapsed after the automobile has been stopped, this voltage has fallen below a predetermined value; and it is decided that there is some fault with the contactor if, even though the time period T2 has elapsed after the automobile has been stopped, this voltage does not decrease at all (for example, refer to Japanese Laid-Open Patent Publication H10-257778).